This invention pertains to the art of conduit couplings, and more particularly to stab-type couplings for use with smooth-walled conduits.
Stab-type couplings permit quick and easy connection of pipes, tubes, and other conduits to a piece of equipment or to another conduit. The conduit to be coupled is cut at a right angle to its lengthwise axis to form a transverse end which is inserted or "stabbed" into a coupling body bore or recess. The coupling includes internal gripping elements that grip the outer surface of the inserted conduit and prevent its withdrawal from the coupling recess. Such a coupling is described in commonly assigned U.S. Pat. No. 4,229,025, the disclosure of which is expressly incorporated by reference herein.
Such couplings have been found to be particularly effective when used to couple lengths of plastic pipe such as that commonly employed in the transmission of natural gas. The coupling body is generally attached at one end to another member such as a male or female threaded member, a T-shaped or L-shaped member, or a like coupling to form a double-ended coupling.
The aforementioned U.S. Pat. No. 4,229,025 discloses a stab-type coupling that has been found to be highly effective and that has enjoyed widespread commercial success, particularly as a coupling for smooth-walled plastic natural gas conduit. Notwithstanding this success, there has been found a need for various improvements to this prior coupling for increased safety and durability with simplified manufacture and decreased cost.
More particularly, there has been found a need for a stab-type coupling for smooth-walled conduit that more effectively seals both the inner diameter of the coupling body recess and the inner diameter of the coupled conduit. With prior couplings, certain defects in the conduit itself may occasionally prevent effective sealing. For example, the conduit may include longitudinal scoring in its outer or inner surface. This scoring in the conduit acts as channels through which gas or other fluid is able to pass between the conduit outer surface and the coupling inner surface, or between the conduit inner surface and a "stiffener" member inserted into the open transverse end of the conduit. Also, it is generally desirable to provide a coupling with redundant sealing, especially when coupling natural gas conduits or the like. In such environments, leakage of the gas can lead to a dangerous situation.
As mentioned, prior couplings do not include redundant seal arrangements where the failure of one seal assembly does not result in fluid leakage. In the case of certain prior hydraulic couplings, for example, a single O-ring seal is provided to seal the inner surface of the coupling body. In the event the single seal fails, fluid leakage will certainly result. Similarly, prior hydraulic couplings that include a conduit inner diameter seal do not include any back-up seal mechanism in the event of seal failure.
Beyond effective sealing, it is critical that a coupling securely retain the conduit in position. In addition, it is desirable to reduce coupling cost and to simplify coupling use and construction. Simplification of construction not only reduces costs, but also reduces the chances for manufacturing defects and user errors.
Accordingly, it has been deemed desirable to develop a new and improved stab-type coupling for smooth-walled conduit that overcomes the foregoing deficiencies and others while providing better and more advantageous overall results.